Catalogs

There are two kinds of unWISE catalogs: individual-image catalogs and band-merged catalogs. The individual catalogs are the outputs of crowdsource on the single-band unWISE tiles. The band-merged catalogs are derived from the individual-image catalogs, merged so that different detections of the same source in different bands are collected together in the same catalog entry. Most users will want the band-merged catalogs.

The band-merged catalogs are very similar to the individual-image catalogs, except most fields have been transformed into two-element vectors, corresponding to the WISE 3.4 and 4.6 micron bands. There is one file for each of the 18240 tiles. The fields are described below. Sizes range from 20 to 60 MB, totaling 541 GB.

The "quality factor" is a concept inherited from PS1. It tabulates the PSF-weighted fraction of pixels contributing to this detection. Good detections will have quality factors close to one. Heavily saturated detections will have quality factors close to zero.

The x and y coordinates are defined so that in Python, image[x, y] gives the value of the pixel (x, y). This means that in terms of layout in memory, the y index increases faster than the x index. This is in contrast to the usual convention, so caveat emptor.

Band-merged Catalogs

Most columns in the unWISE band-merged catalogs are identical to the individual-image catalogs. In these cases, the columns are simply two-element vectors corresponding to the W1 and W2 measurements of a source. These columns are not documented further. A few columns are added, however, and are documented below.

Field Name

Data Type

Description

ra12, dec12

f8

Positions from individual-image catalogs

ra, dec

f8

W1 position, if available; otherwise W2 position

primary12

i2

'primary' status from individual-image catalogs

primary

i2

W1 primary status, if available; otherwise W2 primary status.

unwise_objid

a16

unique object id

Flux Scale

All fluxes are in "Vega nMgy", so that the Vega magnitude of a source is given by \(22.5-2.5\log(\mathrm{flux})\). The absolute calibration is ultimately inherited from AllWISE through the calibration of Meisner et al. (2017). This inheritance depends on details of the PSF normalization at large radii, which is uncertain. To improve the agreement between unWISE and AllWISE fluxes, we recommend subtracting 4 mmag from unWISE W1 and 32 mmag from unWISE W2 fluxes.

unWISE Flags

The unWISE flags simply give the value of the unWISE mask image for the central pixel of the unWISE catalog source, after "collapsing" the time-resolved masks into a smaller number of bits appropriate for static sources. All bits mark features of very bright stars. These flags are described in more detail here.

Bit

Description

0

In core or wings

1

In diffraction spike

2

In ghost

3

In first latent

4

In second latetnt

5

In circular halo

6

Saturated

7

In geometric diffraction spike

Additional Flags

The unWISE info flags contain additional fields related to the crowdsource processing or unWISE coadd bright star mask. These flags are described in more detail here.